The need for boring countersink holes in concrete and other masonary has long existed to meet a variety of needs wherever concrete or masonary is used. Various drilling assemblies for satisfying these needs have been proposed but all are subject to various shortcomings. Typical of these prior proposals are disclosed in U.S. Pat. Nos. to Carver 3,833,073; Salter 3,736,995; Barron 2,978,846 and Crake 2,545,195. Carver proposes a combination drill provided with an inner circular saw cutter specially designed for cutting through metalwork oftentimes employed in concrete building structures having various utility system housings and fittings embedded therein. It has provision for supplying flushing fluid for the core drill but it lacks and has no need for supplying cutting fluid to the circular saw and consequently no need for shifting the flow between these diverse cutters. Salter discloses a core drill with a stepped cutting ring suitable for cutting through a concrete structure and into a metallic utility assembly embedded in the concrete. The smaller diameter cutting ring is used to cut through the metal housing. When the larger diameter portion of the cutting ring contacts the metal fitting a distinctive sound is generated advising the operator that the hole has been cut leaving an inwardly extending metallic flange projecting inwardly from the sidewall of the concrete bore. Barron proposes a drill for hard materials having a stepped cutting end but having no provision for flushing fluid. Crake provides a stepped drill bit of the non-core type with means for drilling a large diameter bore opening at its bottom into a smaller diameter well of predetermined depth. These various prior designs are designed to meet a particular need and are subject to shortcomings and disadvantages avoided by my invention.